Subsea completions and well interventions using a vessel of opportunity

ABSTRACT

A system for performing a desired subsea well-servicing operation, comprises a vessel, a service apparatus for performing the desired subsea well-servicing operation, the service apparatus being supported on the vessel; and a support apparatus mounted on the vessel, the support apparatus having first and second modes, wherein in the first mode the support means does not provide access to a well by the service apparatus and wherein in the second mode the support means does provide access to a well by the service apparatus. The vessel may be a vessel of opportunity and the service apparatus may be selected from the group consisting of subsea tree installation apparatus, perforating apparatus, acidizing apparatus, fracturing apparatus, workover apparatus, reservoir stimulation apparatus, wireline apparatus, coiled tubing apparatus, and snubbing apparatus.

FIELD OF THE INVENTION

The invention relates to a system and method for performing subseacompletions or interventions without using a drilling rig or drill ship.More particularly, the present invention provides a technique by whichequipment needed for subsea well work is provided on a vessel ofopportunity, thereby allowing significant cost savings.

BACKGROUND OF THE INVENTION

Drilling of subsea wells for the production of hydrocarbons typicallyrequires the use of an offshore drilling rig or drill ship, which havethe capacity to support the heavy operations associated with drilling.Because of their technical sophistication and extreme capabilities,drill ships are expensive to build and currently cost on the order of$500,000 per day to operate. In addition, there are relatively few drillships available.

Once a well is drilled, various steps may be performed to prepare thewell for production. These steps are collectively referred to ascompletions and/or interventions. Completion is the process of making awell ready for production or injection, and may include casing andtubing installation or subsea tree installations, perforating,acidizing, or fracturing. In addition, it may be desirable to intervenein a well after production has begun. Such post-production activitiesinclude workover, reservoir stimulation, and other activities, which maybe carried out using wireline, coiled tubing, or snubbing equipment.

Subsea completions are typically carried out using a mobile offshoredrilling unit (MODU), or drill ship. Subsea well interventions indeepwater are commonly carried out using medium intervention vessels orMODUs for the heavier intervention processes such as snubbing andworkover. Because MODU drilling rigs and drill ships are particularlysuited for offshore drilling, they are very expensive and therefore notoptimal for completion or workover activities. Therefore, it isdesirable to provide a system and apparatus that is capable ofperforming completion and/or workover activities without requiring theuse of an offshore drilling rig or drill ship, and that is low cost andlight well intervention equivalent.

SUMMARY OF THE INVENTION

The present invention provides a system and apparatus for completionand/or workover activities without requiring the use of an offshoredrilling rig or drill ship. In particular, the present inventioncomprises the use of modular completion or other equipment inconjunction with a hoist and a vessel of opportunity to reduce the costof various operations below what would be incurred if the sameoperations were carried out using a drilling rig or drill ship. Inaddition, by using modular well-servicing equipment, off-the-shelf hoisttechnologies, and non-dedicated vessels, the present invention frees upexpensive drilling vessels.

In some embodiments, the inventions provides a system for performing adesired subsea well-servicing operation, comprising a vessel, a serviceapparatus for performing the desired subsea well-servicing operation;and a support apparatus mounted on the vessel and supporting the serviceapparatus. The support apparatus has first and second modes such that inthe first mode the support means does not provide access to a well bythe service apparatus and in the second mode the support means doesprovide access to a well by the service apparatus.

The vessel may be a vessel of opportunity and is preferably not a drillship. The vessel may be equipped with one or more position-maintainingdevices. The service apparatus may be selected from the group consistingof subsea tree installation apparatus, perforating apparatus, acidizingapparatus, fracturing apparatus, workover apparatus, reservoirstimulation apparatus, wireline apparatus, coiled tubing apparatus, andsnubbing apparatus.

In other embodiments, the system provides a system for performing adesired subsea well-servicing operation that comprises at least twovessels and a buoyant platform held in place by said vessels, whereinthe platform includes a moon-pool extending therethrough and a rigerected over the moon-pool. The vessels may be vessels of opportunity.

As used herein, “well-servicing” is used to refer to any operation thatmay be performed on an already-constructed offshore well, including pre-and post-production operations, geological and mechanical sidetracks.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more detailed understanding of the invention, reference is made tothe accompanying drawings wherein:

FIGS. 1 and 2 are schematic illustrations of a first embodiment of theinvention in transport and operation modes, respectively;

FIGS. 3 and 4 are schematic illustrations of a second embodiment of theinvention in transport and operation modes, respectively;

FIGS. 5 and 6 are schematic illustrations of a third embodiment of theinvention in transport and operation modes, respectively; and

FIG. 7 is a schematic illustration of a fourth embodiment of theinvention in operation mode.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Referring initially to FIGS. 1 and 2, the present invention includes avessel 10 afloat on the sea surface 20. Vessel 10 is equipped with a rig30 capable of performing one or more desired well-servicing operations.

The well-servicing operations that can be performed by rig 30 includebut are not limited to tubing make-up and running, subsea treeinstallation, perforation, acidizing, fracturing, workovers, reservoirstimulation, wireline operations, coiled tubing operations, andsnubbing.

Vessel 10 can be any vessel that has the capacity to support the desiredwell-servicing operation. Thus, depending on the operation, suitablevessels of opportunity include but are not limited to barges, includinglay barges, bulk carriers, cable ships, container ships, and icebreakers. The variety of vessels that can be used in the presentinvention increases the number of ships that can be considered for agiven operation and eliminates the need for a drill ship or drillingrig, of which there are relatively few. In turn, this reduces the costsassociated with subsea interventions and completions.

In some embodiments, vessel 10 may include a support bracket 32 or thelike, to which rig 30 may be pivotably mounted. Rig 30 is preferably ina horizontal or near-horizontal position during transport, and isrotated as indicated by arrow 37 in FIG. 1 into a vertical position(FIG. 2) after vessel 10 has arrived at the target location above a well(not shown) on the seafloor. Once rig 30 has been rotated into avertical position, it may be supported by bracket 32 and by guy wires38, or any other suitable support mechanism. In the operating position,rig 30 extends off the stern of vessel 10 with sufficient clearance toallow the desired well-servicing operation to be performed. While therig is shown mounted at the stern of vessel 10, it will be understoodthat it could alternatively be mounted on a side or at the bow of thevessel if desired. For the well-servicing operation, rig 30 may beoutfitted with a hoist 34 and/or various other systems 36 that may beneeded to perform the desired operation via riser 40.

In preferred embodiments, vessel 10 is equipped withposition-maintaining devices, such as are known in the art, and/or amooring system. Referring now to FIGS. 3 and 4, an alternativeembodiment of the invention is adapted for use with a coiled tubingsystem 50. Coiled tubing system 50 is preferably mounted on a skid 51and preferably comprises a coiled tubing injector head 52, reel 54 andsupporting equipment 56. As shown in FIG. 4, once vessel 10 has reachedthe target location above a well (not shown), skid 51 is moved laterally(as indicated by arrow 57) until injector head 52 is clear of thevessel, after which coiled tubing well-servicing can proceed in aconventional manner via riser 40.

Another alternative embodiment of the invention includes a supportstructure that can be substantially flattened for transport and erectedfor use once the vessel has arrived at the target location. For example,referring to FIGS. 5 and 6, a structure 60 may include a deck 62supported on a plurality of legs 64 and supporting well-servicingequipment 66 and optional support equipment 68. Legs 64 are lowered orsubstantially horizontal during transport. Once the vessel has arrivedat the target location, structure 60 is erected as indicated by arrow 67and legs 64 are rotated and locked in a vertical position forwell-servicing, which is carried out via riser 40.

Referring now to FIG. 7, still another embodiment of the inventioncomprises a buoyant platform 70 that is held in place by two or morevessels 72. Each vessel 72 is connected to platform 70 by at least oneline 74, and is preferably equipped with a position-maintaining system(not shown).

Platform 70 preferably includes a moon-pool 76 extending therethrough,which provides protected access to the sea from the surface of theplatform. A rig 78 is preferably erected over moon-pool 76. Rig 78 canbe transported to the well site aboard platform 70, or may be erectedafter platform 70 is in position. Rig 78 preferably includes standardrig equipment, including systems necessary for performing the desiredoperation(s). If desired, addition support systems 80 can be provided onone or more of the vessels 72 and connected to the drilling system byflexible lines 82. Once vessels 72 and platform 70 are in position atthe target location, the desired operation can be carried out via riser40.

In each of the embodiments disclosed herein, the rig and/orwell-servicing or well intervention equipment can be commerciallyavailable units that are preferably provided in a modular or turn-keystate. By way of example only, such equipment may include automated pipehandling systems and containerized drilling rigs, such as arecommercially available.

Because the subsea well-servicing equipment used in the presentinvention is modular and can be readily transported and assembled, andbecause vessel 10 is a vessel of opportunity, use of a system inaccordance with the present invention greatly reduces costs andincreases flexibility in subsea well servicing operations.

The present modular subsea completion running equipment can be used incombination with a non-dedicated vessel. The present modules arerelatively easy to transport to different ports around the world for useon vessels of opportunity. This in turn frees up extremely expensivedrilling vessels so that they can be used for drilling, while thevessels of opportunity, at a much lower day rate, can be prepared foroptimum completions. Advantageously, a large percentage of the workrequired to prepare the vessel can be performed in port.

While the present invention has been disclosed and described in terms ofpreferred embodiments, it will be understood that various modificationscan be made thereto without departing from the scope of the claims,which follow. For instance, the support structure can be any suitablestructure, including but not limited to any structure that slides,pivots, or can be assembled in a position such that it overhangs thestern or the side of the vessel so as to provide access to a subseawell.

1. A system for performing a desired subsea well-servicing operation,comprising: a vessel; a service apparatus for performing the desiredsubsea well-servicing operation, said service apparatus being supportedon the vessel; and a support apparatus mounted on the vessel, saidsupport apparatus having first and second modes, wherein in the firstmode the support means does not provide access to a well by the serviceapparatus and wherein in the second mode the support means does provideaccess to a well by the service apparatus.
 2. The system according toclaim 1 wherein the vessel is a vessel of opportunity.
 3. The systemaccording to claim 1 wherein the vessel is not a drill ship.
 4. Thesystem according to claim 1 wherein in the first mode the supportapparatus does not support the service apparatus and in the second modethe support apparatus does support the service apparatus.
 5. The systemaccording to claim 1 wherein the support apparatus supports the serviceapparatus in both the first and second modes.
 6. The system according toclaim 1 wherein in the first mode the support apparatus does not extendover the stern or the side of the vessel and in the second mode thesupport apparatus does extend over the stern or the side of the vessel.7. The system according to claim 1 wherein the service apparatus isselected from the group consisting of subsea tree installationapparatus, perforating apparatus, acidizing apparatus, fracturingapparatus, workover apparatus, reservoir stimulation apparatus, wirelineapparatus, coiled tubing apparatus, and snubbing apparatus.
 8. Thesystem according to claim 1 wherein the support apparatus comprises asupport bracket and the service apparatus comprises a rig pivotablymounted on said bracket, wherein the rig is in a horizontal ornear-horizontal position during transport, and is rotated into avertical position after the vessel is at a desired location, and whereinin the vertical position the rig extends off the stern or side of thevessel with sufficient clearance to allow the desired well-servicingoperation to be performed.
 9. The system according to claim 1 whereinthe support apparatus comprises a skid and the service apparatuscomprises a coiled tubing system mounted on the skid, wherein the coiledtubing apparatus comprises a coiled tubing injector head, a reel andsupporting equipment, and wherein once the vessel is at a desiredlocation, the skid can be moved laterally until the injector head isclear of the vessel.
 10. The system according to claim 1 wherein thesupport apparatus comprises a structure that can be substantiallyflattened for transport and erected for use once the vessel has arrivedat the target location, wherein the service apparatus is mounted on thestructure, and wherein when the structure is erected, the serviceapparatus extends off the stern or side of the vessel with sufficientclearance to allow the desired well-servicing operation to be performed.11. The system according to claim 1 wherein the vessel is equipped witha position-maintaining devices.
 12. A system for performing a desiredsubsea well-servicing operation, comprising: at least two vessels; and abuoyant platform held in place by said vessels, wherein the platformincludes a moon-pool extending therethrough and a rig erected over themoon-pool.
 13. The system according to claim 12 wherein the vessels arevessels of opportunity.